Tap changers for voltage regulation in uninterrupted switching applications using the principle of reactor switching may include one or more vacuum interrupters to prolong the switching life of the device and avoid fouling the dielectric fluid. Vacuum interrupters have been used in load tap changers to regulate the voltage in power transformers for several decades. In U.S. Pat. No. 3,206,580, McCarty describes an invention mechanically linking one vacuum interrupter and two bypass switches. In U.S. Pat. No. 5,266,759, Dohnal and Neumeyer document substantial improvements to such a system. In these examples, complex linkages are used to transmit actuation forces and mechanically synchronize the tap selector, the bypass switches and the vacuum interrupter, which must all be in close proximity to one another. Thus the tap selector, bypass switches and vacuum interrupter are all built into one large assembly, which complicates manufacturing, assembly, and maintenance processes.
In recent years, alternatives have been proposed to simplify the system by decoupling subsystems and using additional motorized actuators. In U.S. Pat. No. 7,463,010, Dohnal and Schmidbauer describe improvements using separate drive systems for various switching subsystems of the tap changer. Alternatively, in U.S. Patent Publication No. 2011/0297517, Armstrong and Sohail describe a system using two vacuum interrupters, one for each moving contact of the tap selector mechanism, with each vacuum interrupter being actuated by a motorized actuator. Both of these solutions provide substantial improvements to simplify the mechanical systems, however it is the point of the present disclosure to provide further improvements. Dohnal and Schmidbauer's invention maintains a level of mechanical complexity within the vacuum interrupter and bypass switch assembly as it relies upon the use of cams and a parallelogram linkage. The two vacuum-interrupter solution provided by Armstrong and Sohail has cost disadvantages due to the expense of using a second vacuum interrupter as well as a robust drive assembly to overcome contact welding since the vacuum interrupters in such a configuration must be able to withstand fault current loads. For overall cost and performance reasons, the use of one vacuum interrupter with two bypass switches is generally accepted as the preferred method.
For background, FIG. 1 illustrates a voltage regulator tap switching circuit, which includes a tap changer 100, a portion of the series winding 220, an equalizer winding 230, a preventative autotransformer 500, and a terminal 410 which could be connected to either the source or load. The series winding 220 and the equalizer winding 230 are integral parts of the voltage regulator's transformer core and coil assembly. The equalizer winding 230 may be omitted from the circuit at the designer's discretion. The preventative autotransformer is a separate subassembly as is the tap changer 100. Within the tap changer assembly 100, there are a plurality of stationary contacts 150, 160, (In certain cases, there are 8 or more stationary contacts connected to the series winding) which are electrically connected to taps in the series winding 220. Movable contacts 110, 120, connect stationary contacts through the preventive autotransformer 500 and equalizer winding 230 to the source or load terminal 410. A prime mover 196, actuates through a mechanical linkage 198, to position the movable contacts 110, 120 on the appropriate stationary contact to regulate the voltage between the source and load.
For further background, FIG. 2 illustrates a common switching circuit for a reactive switching on-load tap changer as is commonly used in a distribution substation transformer. Many items are substantially similar to those of the voltage regulator circuit shown in FIG. 1. However, additional switching components are integrated to eliminate fouling of the dielectric fluid and prolong the switching life of the device. The circuit includes a subassembly 300 consisting of bypass switches 322, 332, and a vacuum interrupter 312. The utilization of these switches is explained thoroughly in U.S. Pat. No. 5,107,200 to Dohnal and Neumeyer. The on-load tap changer consists of both a tap selector switch 101, of a substantially similar design to the tap changer 100 in FIG. 1, and a switching subassembly 300. To actuate and synchronize the switching subassembly 300 to the tap selector switch 101, there is a mechanical linkage 199, which is powered by a single prime mover 196. In practice, the mechanical linkage 199 is a complex design of shafts, gears, cams, bearings and other mechanical components, all of which require a high degree of component-level and assembly-level precision to function properly. Further, the mechanical linkage 199 creates challenges to efficiently packaging the system due to mechanical constraints of power transmission. As a result, there are cost and manufacturing limitations which are improved by the techniques of the present disclosure.